1. Field of the Invention
The present invention relates to a copper alloy with excellent fatigue properties suitable for use in electric devices such as switches and relays to which repeated stress is applied.
2. Discussion of Background
Heretofore, it has been common to use beryllium copper (e.g., Japanese Industrial Standard (JIS) C1720) and phosphor bronze (e.g., JIS C5210, C5191, C5102) as materials for switches, relays and the like, which are used under repetitive stress.
The beryllium copper has the highest strength among copper alloys and excellent properties against repeated stress, so that it has been used as a material for high grade springs in, for example, microswitches. Whereas, the phosphor copper is low in cost and has fairly good fatigue properties, so that it has commonly been used as a material for general-purpose springs in switches, relays and the like.
However, the beryllium copper has a disadvantage of high cost because a component element, Be, is extremely expensive. Whereas, the phosphor copper is far behind the beryllium copper in respect of the fatigue properties though low in cost. Therefore, it has long been desired to have an intermediate material excellent in the fatigue properties and suitable in cost to fill the gap between the beryllium copper and the phosphor bronze.
Further, Cu-Ni-Sn alloys are known as alloys having age-hardening properties through the sprinodal decomposition (see, for example, Japanese Unexamined Patent Publication No. 147840/1980, Bulletin of the Japanese Electronic Materials Society Vol. 15, p13).
These documents disclose Cu-Ni-Sn alloys treated at a high temperature of higher than 800.degree. C. for structure arrangement. Such structure arrangement causes the alloys to be treated in a single phase region.
Such conventional Cu-Ni-Sn alloys have excellent strength after the age-hardening, but they are not substantially different from the phosphor bronze in the fatigue properties. Thus, the conventional Cu-Ni-Sn alloys have a problem that they are not necessarily suitable for use in switches, relays and the like.